This invention relates to improvements in a welded structure in which an outer hollow cylinder of a corrosion resistant metal supporting a stator iron core is welded to an end plate of a base metal disposed at an end of the outer hollow cylinder.
Submersible electric motors to which the present invention is related usually comprises a pair of outer and inner hollow cylinders coaxial with each other, the stator iron core fixedly disposed in an annular space between the outer and inner hollow cylinders, the annular end plate fitted into one end of the annular space and welded to the two cylinders and the bracket fixed to the annular end plate through a plurality of bolts to rotatably support a rotary shaft having a rotor iron core fixed thereon.
In the electric motors as described above, the bracket may become corroded to permit external water to get into the interior of the inner cylinder. The intrusion of the external water affects the electric characteristics of the electric motors less because the interior of the inner cylinder is originally filled with a lubricating liquid. The intrusion of external water into the interior of the outer cylinder, however, results in the occurrence of faults in the electric motors because the stator coil disposed on the stator iron core is not constructed to be water-tight.
In conventional submersible electric motors, therefore, both the outer hollow cylinder and the annular end plate have been formed of a corrosion resistant metal such as a stainless steel, resulting in expensive electric motors. Alternately the end plate-might be formed of a base metal, for example, a general structural rolled steel and that portion thereof contacted by external water coated with an anticorrosive composition. In the latter case, the productivity has been poor because an anticorrosive process is required. Furthermore there have existed the disadvantages that an anticorrosive coating has a short lifetime and the desired anticorrosive effect can not be expected and so on.
Accordingly it is an object of the present invention to provide a new and improved submerged electric motor which is inexpensive and which has improved anticorrosion properties.